1. Field of the Invention
The present invention relates to an acoustic transmitter and an acoustic signal transmission method for transmitting transmission information as acoustic signals. The present invention also relates to an acoustic receiver and an acoustic signal reception method for receiving communication information as acoustic signals. The present invention also relates to an acoustic communication device comprising such an acoustic transmitter and acoustic receiver, and an acoustic signal communication method.
The present invention also relates to a program product for a computer installed in an acoustic transmitter.
2. Description of the Related Art
A remote monitoring/control system which transmits an amount of gas consumption of each home (residence) to a center station for automatic meter reading and collection, notifies of a gas leak when it occurs, or shuts off the gas meter by remote control from the center station responding to gas leak notification, has been in practical use.
For such a remote monitoring/control system, a microcomputer having communication functions or the like is disposed in a gas meter installed at each home (residence). The microcomputer or the like of the gas meter is connected to a terminal network control device via a wire line, and the terminal network control device is connected to the center station via a telephone line.
For this, a through hole is constructed in each residence to pass through the wire line connecting the gas meter and the terminal network control device. This construction, however, is often difficult especially for multiple dwelling homes, and in some cases damages the visual appearance of the building.
An alternative idea is connecting the microcomputer or the like of the gas meter to the terminal network control device via wireless communication, such as a radio wave, and connecting the terminal network control device to a telephone (stationary telephone) of each home, so as to be connected to the center station via the telephone line. Recently, however, customers who have no telephones at home are increasing because of the spread of portable telephones and PHS, so such a method of using a radio wave can not be applied to all residences.
A decrease in the cost of such communication equipment is also demanded.
For this, an acoustic signal communication method for propagating the communication information inside a gas pipe or the like as acoustic signals, is under consideration. In this method, such communication information as meter values, gas leak occurrence notification and the like is transmitted from a gas meter installed at one end of a gas pipe to a terminal network control device installed at the other end of the gas pipe by acoustic signals.
When communication is performed by acoustic signals inside a gas pipe, however, reverberation waves (delay waves) are generated due to the reflection of sound at the bending section and branching sections of the pipe, for example. Therefore if communication information is continuously transmitted, acoustic signals transmitted later are interfered with by the reverberation of the previously transmitted acoustic signals, and the reception side can not accurately receive acoustic signals.
To prevent this influence of reverberation, it is necessary to wait until the reverberation of previously transmitted acoustic signals is attenuated to a predetermined level or less before transmitting the next acoustic signals. Therefore an acoustic communication based on simple pulse signals has limitations in improving transmission speed.
On the other hand, it has also been attempted to modulate pulse signals by Gaussian window signals before transmission so as to be less influenced by reverberation waves, where a certain improvement of transmission speed has been confirmed, but there is a demand to further improve the transmission speed.